[PM-WIP-OPP] [PATCH] cleaner ceil function for uv to vsel conversion

[PM-WIP-OPP] [PATCH] cleaner ceil function for uv to vsel conversion

[Romit Dasgupta]

Cleaner ceil function.
Signed-off-by: Romit Dasgupta <romit@ti.com>
---
diff --git a/arch/arm/plat-omap/opp_twl_tps.c b/arch/arm/plat-omap/opp_twl_tps.c
index e0db39b..1caa414 100644
--- a/arch/arm/plat-omap/opp_twl_tps.c
+++ b/arch/arm/plat-omap/opp_twl_tps.c
@@ -36,14 +36,7 @@ unsigned long omap_twl_vsel_to_uv(const u8 vsel)
  */
 u8 omap_twl_uv_to_vsel(unsigned long uv)
 {
-	u8 vsel;
 
-	vsel = ((uv / 100) - 6000) / 125;
+	return (((uv + 99) / 100 - 6000) + 124) / 125;
 
-	/* round off to higher voltage */
-	/* XXX Surely not the best way to handle this. */
-	if (uv > omap_twl_vsel_to_uv(vsel))
-		vsel++;
-
-	return vsel;
 }

Re: [PM-WIP-OPP] [PATCH] cleaner ceil function for uv to vsel conversion

[Kevin Hilman]

Romit Dasgupta <romit@ti.com> writes:

> Cleaner ceil function.

Needs better subject and better changelog.

Subject should probably be something like: OMAP: 

  [PATCH] OPP: TWL/TPS: optimize uv to vsel function

And changelog should describe the motiviation for the patch or a
description of the problem you're trying to solve.  IOW, is this a
correctness fix, or an optimization, etc.  Looks to me like it's tring
to compensate for some rounding issues, but please describe in detail
in the changelog.

Thanks,

Kevin


> Signed-off-by: Romit Dasgupta <romit@ti.com>
> ---
> diff --git a/arch/arm/plat-omap/opp_twl_tps.c b/arch/arm/plat-omap/opp_twl_tps.c
> index e0db39b..1caa414 100644
> --- a/arch/arm/plat-omap/opp_twl_tps.c
> +++ b/arch/arm/plat-omap/opp_twl_tps.c
> @@ -36,14 +36,7 @@ unsigned long omap_twl_vsel_to_uv(const u8 vsel)
>   */
>  u8 omap_twl_uv_to_vsel(unsigned long uv)
>  {
> -	u8 vsel;
>  
> -	vsel = ((uv / 100) - 6000) / 125;
> +	return (((uv + 99) / 100 - 6000) + 124) / 125;
>  
> -	/* round off to higher voltage */
> -	/* XXX Surely not the best way to handle this. */
> -	if (uv > omap_twl_vsel_to_uv(vsel))
> -		vsel++;
> -
> -	return vsel;
>  }

Re: [PM-WIP-OPP] [PATCH] cleaner ceil function for uv to vsel conversion

[Romit Dasgupta]

Kevin Hilman wrote:
> Romit Dasgupta <romit@ti.com> writes:
> 
>> Cleaner ceil function.
> 
> Needs better subject and better changelog.
> 
> Subject should probably be something like: OMAP: 
> 
>   [PATCH] OPP: TWL/TPS: optimize uv to vsel function
> 
> And changelog should describe the motiviation for the patch or a
> description of the problem you're trying to solve.
The description of the problem is "Cleaner ceil function for uv to vsel
conversion".

I think this patch is simple enough for people on this list to understand the
optimization. I am sorry I cant be more descriptive.

> IOW, is this a
> correctness fix, or an optimization, etc.  Looks to me like it's tring
> to compensate for some rounding issues, but please describe in detail
> in the changelog.

Re: [PM-WIP-OPP] [PATCH] cleaner ceil function for uv to vsel conversion

[Nishanth Menon]

Romit Dasgupta said the following on 01/12/2010 02:58 AM:
> Kevin Hilman wrote:
>   
>> Romit Dasgupta <romit@ti.com> writes:
>>
>>     
>>> Cleaner ceil function.
>>>       
>> Needs better subject and better changelog.
>>
>> Subject should probably be something like: OMAP: 
>>
>>   [PATCH] OPP: TWL/TPS: optimize uv to vsel function
>>
>> And changelog should describe the motiviation for the patch or a
>> description of the problem you're trying to solve.
>>     
> The description of the problem is "Cleaner ceil function for uv to vsel
> conversion".
>
> I think this patch is simple enough for people on this list to understand the
> optimization. I am sorry I cant be more descriptive.
>
>   
here is a try:
-----

 From patchwork Thu Dec 31 13:29:05 2009
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Subject: [pm-wip-opp] [PATCH] opp: twl/tps: optimize uv to vsel function
Date: Thu, 31 Dec 2009 13:29:05 -0000
From: Dasgupta, Romit <romit@ti.com>
X-Patchwork-Id: 70374


For integer values x and y; int div x / y causes truncation. Current
omap_twl_uv_to_vsel function implements an equivalent of ceil which
is based on an if condition to check truncation and round up.
We can do this in a more optimal manner without the if condition.
The round up is handled by adding the round off factor prior to
truncation as:
(x + (y - 1)) / y

---
Currently putting signed-off in --- section. If Romit is ok, please 
re-send as needed.
Signed-off-by: Dasgupta, Romit <romit@ti.com>

diff --git a/arch/arm/plat-omap/opp_twl_tps.c 
b/arch/arm/plat-omap/opp_twl_tps.c
index e0db39b..43dee2d 100644
--- a/arch/arm/plat-omap/opp_twl_tps.c
+++ b/arch/arm/plat-omap/opp_twl_tps.c
@@ -36,14 +36,7 @@ unsigned long omap_twl_vsel_to_uv(const u8 vsel)
  */
 u8 omap_twl_uv_to_vsel(unsigned long uv)
 {
-    u8 vsel;
+    /* Takes care of precision loss due to integer division */
+    return (((uv + 99) / 100 - 6000) + 124) / 125;
 
-    vsel = ((uv / 100) - 6000) / 125;
-
-    /* round off to higher voltage */
-    /* XXX Surely not the best way to handle this. */
-    if (uv > omap_twl_vsel_to_uv(vsel))
-        vsel++;
-
-    return vsel;
 }

Re: [PM-WIP-OPP] [PATCH] cleaner ceil function for uv to vsel conversion

[Romit Dasgupta]

>> The description of the problem is "Cleaner ceil function for uv to vsel
>> conversion".
>>
>> I think this patch is simple enough for people on this list to understand the
>> optimization. I am sorry I cant be more descriptive.
>>
>>   
> here is a try:
> -----
> 
>  From patchwork Thu Dec 31 13:29:05 2009
> Content-Type: text/plain; charset="utf-8"
> MIME-Version: 1.0
> Content-Transfer-Encoding: 7bit
> Subject: [pm-wip-opp] [PATCH] opp: twl/tps: optimize uv to vsel function
> Date: Thu, 31 Dec 2009 13:29:05 -0000
> From: Dasgupta, Romit <romit@ti.com>
> X-Patchwork-Id: 70374
> 
> 
> For integer values x and y; int div x / y causes truncation. Current
> omap_twl_uv_to_vsel function implements an equivalent of ceil which
> is based on an if condition to check truncation and round up.
> We can do this in a more optimal manner without the if condition.
> The round up is handled by adding the round off factor prior to
> truncation as:
> (x + (y - 1)) / y
> 
Wow that is nice... Please send it if you can and add your Signed-off  for the work!